Low friction coatings allow contacting surfaces to rub against one another with reduced friction, reducing the effort to move garment treatment appliances, like dewrinkling devices, such as an iron, or a steamer. Further, a scratch resistant coating is very important for electrical appliances, and also for non-electrical domestic appliances, such as pans, oven plates and the like, that benefit from low friction. Hence the use of a coating with low friction co-efficient and good scratch resistance, to improve the tribological properties of appliance surfaces is constantly increasing.
An example of a treatment plate for a garment treatment appliance for treating garments is the soleplate of an iron. In general, a separate layer, here referred to as a coating layer, is applied to the surface of the soleplate facing away from the housing of the iron. During ironing, this coating layer directly contacts the clothes to be ironed. A prerequisite for the proper functioning of the iron is that such a coating layer meets a large number of requirements. For example, the coating layer must, inter alia, exhibit satisfactory low friction properties on the clothes to be ironed, it must be corrosion-resistant, scratch-resistant, and durable, and exhibit an optimum hardness and high resistance to wear and to fracture. The material of the coating layer must meet extra high requirements because the coating layer is exposed to substantial variations in temperatures ranging between 10° C. and 300° C., with typical operational temperatures ranging from 70° C. to 230° C. The required gliding behavior is obtained by having a low friction providing coating on the soleplate and this reduces the effective force applied on the garment as well.
Several materials may be used as low friction soleplate coating materials for an iron, such as silicates applied via sol-gel techniques, enamel, metal (e.g. nickel, chromium, stainless steel) that may be applied, for example, as sheet material or by thermal spraying, hard anodized aluminum, and diamond-like carbon coatings. Also an organic polymer may be used as a soleplate coating, for example polytetrafluoroethylene (PTFE). The PTFE low friction coating shows good gliding and non-stick properties, however the mechanical properties like scratch and wear resistance of PTFE coating is poor.
Another type of low friction coating has been disclosed in U.S. Pat. No. 5,943,799 A1, the low friction layer consists predominantly of aluminum oxide which is formed in an electrochemical manner, and the low friction coating shows good gliding behavior, as well as good scratch resistance and easy to clean. However, the substrate used for forming of the low friction metal oxide coating has to be the same metal, which is aluminium in this case, and restricts the application of the coating.
A sol-gel coating for use on irons is disclosed in U.S. Pat. No. 5,592,765. The sol-gel coating shows good properties such as good wear and scratch resistance, as well as good stain resistance.
U.S. Pat. No. 7,339,142 discloses an iron having a soleplate covered with a coating consisting of an external layer, comprising at least one oxidation catalyst chosen among oxides of platinoids, and at least one internal layer, located between the metal support and the external layer, comprising at least one oxidation catalyst chosen among the oxides of the transition elements of group 1b. Platinoids are, in this reference, deemed to be elements having properties similar to those of platinum, in particular, in addition to platinum, ruthenium, rhodium, palladium, osmium, and iridium, thus elements of groups 8-10 of the periodic table. The coating is claimed to be self-cleaning, at the operating temperature of the device.
An iron having a soleplate with an oxidation catalyst present on the outer surface of the soleplate is known from U.S. Pat. No. 7,040,047. The catalytic oxidation agent is, according to this reference, any element, compound or composition capable of oxidizing, at a temperature at least equal to 90° C., any organic substance such as contained in the dirt, or stains, presently encountered in the treatment (including washing and possibly softening) of textile articles or pieces (for example linen). As examples of catalytic active elements, palladium, platinum, vanadium, and copper are mentioned. To increase the catalytic effectiveness, oxides of copper, manganese or cobalt can be present. The catalytically active form of the oxidation agent, for example platinum, can be obtained by calcination. This reference also mentions by way of example, that the catalytic oxidation agent comprises a metal of group IV of the periodic table; the use of these metals has nevertheless not been illustrated.
The teaching of the above references is that “organic dirt” captured by the soleplate during ironing is oxidized so that it will be detached from the soleplate. It is said that even when the soleplate is tarnished in a manner that is hardly visible, it will partially lose its sliding qualities. Imperceptibly, with the soiling, the ironing will become more difficult, while the user will become apprehensive of using a tarnished iron, fearing that it can alter the laundry.
US 2013/0247430 describes a heating appliance including a metal substrate, at least a part of which is covered with a self-cleaning coating including at least one oxidation catalyst selected from the platinoid oxides, and at least one dopant of said oxidation catalyst selected from the rare-earth oxides. The self-cleaning coating is a bilayer coating including: an inner layer at least partially covering the metal substrate and including the dopant; and an outer layer in contact with the ambient air and including the oxidation catalyst. Also provided is a method for producing such a heating appliance.
U.S. Pat. No. 4,665,637 describes a fabric pressing device having a composite sole plate with a base component of metal or similar thermally conductive material that is coupled to the heat source of the pressing iron, and a layer of ceramic bonded to the base component. The ceramic layer has a planar fabric pressing surface that preferably has a smoothness of about a nominal two micrometers surface roughness or better. That ceramic surface is highly resistant to wear and to impact, is easy to clean, and has excellent dynamic and static frictional characteristics on textile fabrics.